Leak down test

So I finally got a hold of some fittings that I could use to make up a leak down tester from a HF compression tester. Back a few weeks ago when I did the compression test all the cylinders were between 475 to 500 psi, except for cyl #2 which was 420. I did a leak down test today on #2 and while the bleed off was very slow you could hear the air escaping from 3 ft away. I pulled the valve cover, then took the rockers off #2 so the valves would be closed. I could hear air in the exhaust manifold, and up on top near the springs. But I also could hear air when I took off the oil fill cap too. It might have been an echo of the air escaping, but that's what I wanted to ask. If air is getting by the intake or exhaust valve, could it make it down to the case. There's where the blowby I'm getting could be coming from. What do you guys think?

If you're hearing air escaping by the springs, that's underneath the valve cover. In that case, it will get into the crankcase by going through the oil drain back holes in the heads. What that means is that you have valve guide issues which makes perfect sense on a 7.3. The next step will be chuffing. It's not bad right now, but it won't get any better on it's own.

Bronco, I have the valve cover off. I pulled the rockers to close the valves. This is on my 6.9. I sold the 7.3. It sounds like air is going into the exhaust manifold, and I'm getting some sound thru the oil fill. No noise thru the dip stick.

Ok sorry about that. If air is going into the exhaust, your exhaust valve isn't sealing. You did mention that you could hear air coming out up by the valve springs. You could test this by taking some WD-40 (or something similar) and spraying it around the valve guides while you're pressurizing the cylinder to see if you can see some bubbles. I suggest the WD-40 over soapy water since the WD-40 is oily. Air coming from the oil fill could be just from air getting through the large ring gaps that these engines have. If you can see bubbles around the valve guides, then you would have extra blow by compared to normal.

I picked up a fel pro gasket kit, seals and all. Going to pull the heads next week. Need to find a shop crane hoist thing; maybe a neighbor has one. My back isn't up to that weight anymore. First I need to find a place that will do the valves.

quickster said:

First I need to find a place that will do the valves.

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Make sure that you can trust that place too. Otherwise you may end up overhauling your engine to make sure that there's enough valve clearance. That's what I had to do in order to put some decomp pistons in it.

While the heads are off, is easier to reseal the oil cooler also in the truck.

Hey quickster, would it be possible to get some pics of the leak down tester you made from the HF compression tester. Sounds like this i what I need to evaluate my issues with blow-by. Thanks!

The tester is a HF, I think it cost $25. The diesel specific one. Diesel Engine Compression Tester 20 Pc. Once you get it you need to see the type of quick connect fittings it has. I think that they are not all the same. I had to buy this SPARC 6pc Inert Gas Quick Connect Kit 1/8" NPT (New) on Amazon. The fitting that goes in the glow plug hole that comes with the compression tester mates to the female connector. Then all you need is an in line regulator to slowly add air. Or pick up a cheap HF leak down tester. The only reason the leak down tester didn't work on it's own is the funky air connection size. Otherwise it should have worked right out of the box. The compression test fitting are good to 1000 psi-that's why the specific connectors. I didn't need to read any gauges-- I could hear the air leaking from the cylinder 2 feet away. Do the compression test, then figure out what cylinder to zero in on.
Rip, I had the pleasure of resealing the oil cooler months ago. lol

Thanks for the info quickster! Looking forward to see what results show up on mine with the leak down test. Ill be watching this thread for sure.